The present invention relates to a radiation-sensitive mixture containing a polymeric binder having acid-cleavable side groups and a compound that forms a strong acid on irradiation. It also relates to novel amides of .alpha.,.beta.-unsaturated carboxylic acids with which the polymers used as binders are synthesized.
Radiation-sensitive mixtures are known per se. Commercially-available, positive-working mixtures are especially used as resist material. These contain, in addition to o-quinone diazide, a binder that is soluble in aqueous-alkaline solution, such as poly(4-hydroxystyrene) or a novolak. The sensitivity of these systems to radiation, particularly short-wave radiation, is sometimes unsatisfactory. As a result of the high intrinsic absorption in the UV-2 range (220-300 nm), novolaks are unsuitable as binders in a single-layer resist material for deep-UV lithography (220-330 nm). Poly(hydroxystyrene) has, on the other hand, more favorable absorption properties in the UV range. It also has a higher thermal stability. However, this polymer can only be obtained by elaborate multistage syntheses. Its lithographic properties are also unsatisfactory in both 3-component systems and 2-component systems because of a poor hydrophilic/hydrophobic balance. There is therefore a need for binders for high-resolution, high-sensitivity resist materials that have good etch resistance, good transparency and high thermal stability for UV-2 lithography and that can be developed in aqueous-alkaline solutions.
It is also known to increase the radiation sensitivity of radiation-sensitive mixtures by adding a compound that, on exposure to radiation, releases an acid that then catalyzes secondary reactions. Such compounds are, for example, diazonium, phosphonium, sulfonium and iodonium salts, nitrobenzyl esters, phenolic methanesulfonates and diazo and halogen compounds. The use of the onium salts as photochemical acid formers in resist materials is disclosed, for example, by U.S. Pat. No.4,491,628. A review of the use of onium salts in resist materials is given by Crivello in Org. Coatings and Appl Polym. Sci., 48: 65-69 (1985).
Radiation-sensitive mixtures of polymers containing acid-labile side groups and photochemical acid formers are disclosed by U.S. Pat. No.4,491,628 and FR 2,570,844 (.apprxeq. U.S. Pat. Nos.4,689,288 and 4,770,977). Only polymers of p-substituted styrene or .alpha.-alkylstyrene are disclosed in the two publications mentioned. Tert-butoxycarbonyloxy and trialkylsilanyloxy groups are identified as acidlabile p-substituents. These polymeric binders are hydrophobic and become soluble in alkali only after exposure.
Copolymers containing acid-labile groups that are bound via a phenolic oxygen atom, for example, copolymers of p-hydroxystyrene and tertbutoxycarbonyloxystyrene, are disclosed in J. Poly. Sci., Part A, Polym. Chem. Ed., Vol. 24: 2971-80 (1986).